Merge branch 'add-start-to-plugins' into ebean-new

# Conflicts:
#	ebean-core/src/main/java/io/ebeaninternal/server/core/DefaultServer.java
#	ebean-ddl-generator/src/main/java/io/ebeaninternal/dbmigration/DdlPlugin.java

ebean-api/src/main/java/io/ebean/plugin/Plugin.java

@@ -14,6 +14,13 @@ public interface Plugin {
    * Called just before the server starts indicating if it is coming up in online mode.
    */
   void online(boolean online);
+  
+  /**
+   * Called when server.start is invoked. This may be executed for each tenant.
+   */
+  default void start() {
+    
+  };
 
   /**
    * Called when the server is shutting down.